Is one who is unable to attend congregational prayers – due to the difficulty of obtaining his manager's permission – sinful, even though the mosque is only a 4-minute walk away?

Congregational prayer is permissible outside the mosque. If an employee is unable to perform it at his workplace, he should advise his employer and explain the virtue of congregational prayer. He should not be prevented from it except for a valid excuse, such as the risk of financial loss, the mosque being far away, or the Imam prolonging the prayer. If the employer insists on preventing it, there is no harm for the employee to continue in this job. However, if he finds another job where he can maintain congregational prayer, that is more preferable.